1. Field of the Invention
This invention relates to a dielectric ceramic and a process of preparing it, and is more particularly concerned with a dielectric ceramic having high dielectric constant and high unloaded Q, and a process of preparing the same.
2. Description of Prior Art
In general, dielectric ceramics having high dielectric constant and high unloaded Q, and yet having a small absolute value for the temperature coefficient of resonance frequency, are desired to be used in dielectric resonators or dielectric substrates used in signal circuits in the region of high frequencies such as microwaves and millimeter waves. TiO.sub.2 materials have hitherto been widely used as the dielectric ceramics of this type, as exemplified by BaO--TiO.sub.2 or ZrO.sub.2 --SnO.sub.2 --TiO.sub.2 materials, and Ba(Zn,Ta)O.sub.3 or Ba(Mg,Ta)O.sub.3 materials have been recently used. The dielectric ceramics comprised of these mateials have characteristics such that at a high frequency of about 10 GHz the unloaded Q ranges from 3,000 to 7,000, the dielectric constant ranges from 20 to 40 and the temperature characteristic of resonance frequency is considerably so small as to be nearly 0 ppm/.degree.C.
These dielectric ceramics have been prepared by making a powdery raw material mixture which is uniform in the composition according to a coprecipitation method, a multi-stage wet method or the like, calcining, grinding and thereafter pressure-molding the powdery raw material mixture, followed by firing of the resulting pressure-molded product over a long period of time, e.g., 140 hours.
The above conventional preparation process requires a number of progressive steps and also requires the strict controlling of preparation conditions. Hence, process management is complicated, and also there is a problem in mass production.